International Standard Book Number: a 13- or (if assigned prior to 2007) 10-digit identifying number assigned by the publishing industry to a published book or similar item, registered with the International ISBN Agency.

ISSN

International Standard Serial Number: an eight-digit number to uniquely identify a serial publication.

DOI

Digital Object Identifier: a unique string of letters and numbers assigned to an electronic document.

URI

Uniform Resource Identifier: a string of characters to uniquely identify a resource which usually contains indication of the means of accessing that resource, the name of its host, and its filepath.

VIAF

A data number in the Virtual Internet Authority File assigned to link different names in catalogs around the world for the same entity.

ESTC

English Short-Title Catalogue number: an identifying number assigned to a document in English printed in the British Isles or North America before 1801.

OCLC

OCLC control number (record number) for the union catalog record in WorldCat, a union catalog for member libraries in the Online Computer Library Center global cooperative.

idno should be used for labels which identify an object or concept in a formal cataloguing system such as a database or an RDF store, or in a distributed system such as the World Wide Web. Some suggested values for type on idno are ISBN, ISSN, DOI, and URI.